Mexico has one of the highest murder rates in the world, but who cleans up the blood at the crime scene when the police and investigators have left? Donovan Tavera is Mexico's first forensic cleaner. As he explains here, his fascination with blood began as a young boy.
What happens to the blood after a murder? The question haunted me for years, until I answered it myself.
The first time I saw a dead body was when I was 12 years old. Early one morning we heard that somebody had died on the street outside our block of flats. We went out to look. There were clear signs of violence. The man didn't have a shirt. I was struck by the streams of blood going down the street. But I didn't feel scared - I was just very curious. And that's how my fascination with blood began.
As well as us bystanders there were police officers and investigators. I kept waiting for someone to come and clean up the blood, but no-one came. Some of the blood even ran towards our building and my mother washed it away with water.
I asked her: "Who cleans the blood after a murder?" I asked her so many questions that day.
When my father came home from work I asked him too: "What happens to the blood after a murder? How do you clean it up?" I kept asking about it for days, until he said, "Please stop talking about this. Enough!"
That was when I decided to find out for myself. I went to the library and took out a book on medicine, but that was too general. Then I found a book about forensic medicine. I read about the process of death and what happens to a corpse. I learned a lot.
A murder isn't the same as an accident - in a murder there is a lot of blood. And blood can carry diseases. It seemed to me that if someone takes bodies from the street, there should also be a professional who cleans up the blood.
When I was about 17 I started experimenting. I went to the butcher and bought cow's liver and bones and then at home I would investigate how to clean up the blood.
And that's how I became a forensic cleaner.
Over the years I have invented more than 300 different formulas to clean up blood. Some I have perfected over the years. Others haven't changed since I first used them.
You need different methods depending on what you are cleaning - whether it's the carpet of a car, for instance, or personal objects like watches or rings. It also depends on how and when the person died. For instance, someone may have been lying dead in the bathroom of their house for a week, in a humid environment. In another situation, perhaps where a man has hung himself with his own tie, you need to consider other bodily fluids such as semen or faeces.
Before I come I ask what happened, and where the corpse is. I also need to know if the dead person was ill, and if there is a chance of contamination. That way I can plan ahead.
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I am the last person to visit the scene of the crime. I come after the police officers have left, and after the funeral has taken place. I am the last person associated with what happened, and often the dead person's family use me as a bit of a therapist. In the beginning I used to get personally affected, but now I listen politely and then get on with my work.
I usually work with my headphones on because music helps me concentrate. I always listen to the same three things: Tristan und Isolde by Wagner, 666 Number of the Beast by Iron Maiden and Paranoid by Black Sabbath. The opera relaxes me, it helps me concentrate and prepare mentally. But once I put my uniform on and start cleaning, I want to listen to heavy metal.
My work can only begin once the authorities have issued a legal statement saying someone outside the police investigation is allowed on the scene of the crime. Without that piece of paper, I can't do my job.
A few times people have called me to do a job, but when I asked them for those legal documents, they didn't have them. Instead, they offered me money - good money. When I told them I couldn't work without the proper authorisation, they quickly hung up. They may have been criminals, or perhaps it was a joke, I don't know.
The people who hire me are going through a very painful situation. From the moment the dead body is found until I have finished, they have to live with the blood - on the floor, on the walls, in the bathroom. And it smells. So when the house is clean and the smell has gone, their mood changes. Often, they cry with relief - a burden has been lifted. They no longer have to live with that shocking scene. It still hurts, but it's one less burden to carry.
The worst crime I've had to clean up was a multiple homicide in Mexico City where four people died. They were stabbed and the traces I saw showed signs of self-defence and panic. There was a lot of anger and desperation at that scene. It took us more than 10 hours to clean it - we had to hand over the house on the same day. My client was devastated, but in the end we gave back a place without a single trace of what had happened. My work had helped in some way and afterwards the person thanked me in a very nice way. There was a totally different atmosphere - it felt light, as if what had happened had happened a long time ago, like a distant memory.
I never thought this would be how I earn my living. I didn't even know this profession existed until I taught myself how to do it.
All photographs by Benedicte Desrus
Listen to Donovan Tavera speaking to Outlook on the BBC World Service